Sam Shepard doesn't have a lot to say about "The Late Henry Moss," his play that premieres this week, presented by the Magic Theatre at Theatre on the Square. But with his respected reputation as a playwright - and a heavyweight cast including Sean Penn, Nick Nolte, Woody Harrelson and Cheech Marin - he doesn't have to.

Shy, taciturn and famously resistant to anything that carries the whiff of celebrity, Shepard is hardly an interviewer's dream. During a conversation at the Magic Theatre's performing space at Fort Mason, the Pulitzer-winning playwright munches on a sandwich and looks down, avoiding eye contact, when a question is asked.

"It's basically messing around with the same things I've always been fooling with over the years," he allows during a rehearsal break. "Brothers and fathers and all that stuff. I don't want to get too specific about it."

He's not rude, just remote. It's always been that way with Shepard, a man so gifted, so charismatic and so private that he's inadvertently created a mystique around himself - a mystique that perpetuates the public fascination that he shuns.

The mystique is fueled by his rock-star looks. As a young man, Shepard was flat-out beautiful. As he aged and grew into the lean, weathered figure that he is now - he turns 57 today - Shepard took on an iconic quality, like one of the lonely, rough-hewn characters in his plays.

Shepard doesn't answer personal questions... And he's predictably dodgy on the subject of his play: "I don't want to give a lot of it away, to tell you the truth," he says.

This much, one gathers, is true: "The Late Henry Moss" is a family drama, set in the New Mexico desert or, more accurately, in the mythical American West that is Shepard's spiritual terrain. There is an old man played by James Gammon, the gravel-voiced character actor who appeared in the 1996 Broadway revival of Shepard's "Buried Child" and plays Don Johnson's crusty dad on "Nash Bridges."

There are his two estranged sons, Ray and Earl, played by Penn and Nolte, who return to the father's house and confront their conflicted and violent past; a gabby cabdriver, played by Harrelson, who carries an important piece of information; a neighbor, played by Marin, who's a friend of the old man's; and the old man's young girlfriend (Sheila Tousey).

Asked how the play differs from his earlier work, Shepard answers, simply, "It specifically deals with death. I've never directly dealt with that. The other (plays) have that peripherally, but this is the centerpiece of it."

Beyond that, Shepard is mum. According to Magic Theatre artistic director Larry Eilenberg, the playwright called him a year ago to propose a "Henry Moss" premiere.

"It's my understanding that he had been working toward this play 10 years ago, and then it became active again," Eilenberg says. "What he presented was an unfinished script and an idea of doing it here. Even then he had some strong casting ideas -- and some of them are in this cast."

When Eilenberg read the finished work, he says, "I was hugely enthused. I think it's an important work, and a deeply American work. This is one of our great playwrights working at his best."

Shepard and the Magic have a long history, starting in the 1970-71 season when the theater, located at that time in Berkeley, produced Shepard's "La Turista." The Magic also premiered "Buried Child" in 1978, which won a Pulitzer the next year; "True West," with Peter Coyote and Jim Haynie, in 1980; and "Fool for Love," with Ed Harris and Kathy Baker, in 1983. Not counting "Henry Moss," 15 Shepard productions have been mounted at the Magic, most recently "Eyes for Consuela" in February 1999.

In 1998, the theater renamed one of its stages the Sam Shepard Theatre and celebrated the occasion with a four-day marathon of plays dubbed Samfest.

That's a rich, sustained relationship, and yet "Henry Moss" marks the first time Shepard has directed a play here since "Fool for Love." He says the decision had nothing to do with the poor reviews that his previous two plays, "Simpatico" and "Eyes for Consuela," received in New York, or the chance to work in San Francisco, where the scrutiny is presumably less intense. As it happens, geographical distance hasn't protected "Henry Moss" from the eyes of the world: The New York Times, Los Angeles Times, USA Today, Associated Press and Newsday will all be covering the play's opening.

"A lot of it had to do with convenience," Shepard says, "because Sean was pretty much stationed here and he didn't really want to leave the area. And then, I thought it would be great to return here after so many years."

After 37 years of writing plays, Shepard says he enjoys it as much as ever. Theater is a touchstone for him, an antidote to the artificiality of popular culture and the glib distractions of the technological world. "I don't expect it to be a cure," he says, "but theater is a way in which human beings face each other directly. That's what it's all about."

In a theater, he says, audience members "don't have a remote control. There's no screen, nothing standing between, no filtering. It's right there in front of you. And I think that's the real power of theater, that it reconnects people with people."

In a 1996 interview, Shepard lamented the gradual erosion of human connection through technology. "Betrayal is in my bones, somehow," he said. "It's something that has not only affected me personally, but is in the whole fabric of the culture. . . . We don't seem to be able to face what has actually become of us."

He listens to that quote as it's read back to him and nods. "I find it even truer now," he says. "I think the betrayal becomes more and more outrageous as we go on, particularly with the electronic revolution. We prefer the cellular world and all the tricks that electronics can do to human beings. We don't want to deal with flesh and blood. . . . It's so extreme that we don't even realize it's a betrayal."

Shepard says he finds solace in making theater, in listening to music and in reading. He finds it in the life he's created with Lange on their 400-acre horse and cattle ranch. "I think the country helps a great deal," he says. "I'm involved with livestock, and I like having space around, a lot of space."

"I guess I'm fairly reclusive," he says when asked about his reputation as a man apart. "I think it's important to maintain. Nothing is private anymore. Everything is accessible. The Internet and all that s--. It just makes me a little bit crazy."

One has to wonder why, if Shepard dislikes the life of the famous person so much - and feels "diminished," as he once said, by having a public image - he continues to make movies. He became a movie star with Terrence Malick's "Days of Heaven" in 1978, and he's averaged one film per year ever since.

"I'm subsidizing my playwriting," he says. "You don't make a whole lot of money writing plays. From the get-go I was terrified of becoming a movie star, to tell you the truth. Because I considered myself a playwright, and I still do. And I was afraid in a way that if I went too far with that, that I would no longer be taken seriously as a writer."

Shepard's fears didn't come true, and his position as one of the country's premier playwrights was only solidified with the Broadway revivals of "Buried Child" and "True West." It's an amazingly long and fertile writing career, not without its rough patches, that seems undiminished by Shepard's movie stardom or the nagging considerations of celebrity.

As the interview draws to a close and Shepard gets up to return to his rehearsal -- to another round with his actors and the unseen demons that populate "The Late Henry Moss" -- he seems relieved. "Sorry to be so reticent in certain areas," he says.